1. Field of the Invention
The present invention relates to a method for preparing composites of substrate-molecular sieve.
2. Description of the Related Art
Zeolite is a generic name of crystalline aluminosilicate, which constitutes the pore skeleton of zeolite molecules and bears an anionic charge for each aluminum atom. Cations for offsetting such anion charges are present within the pore space and the remaining pore space is filled with water. Where zeolite is heated for a given period of time at 200-300° C., anions or water molecules are released, rendering it to accept other molecules into its pores. Such acceptance ability allows zeolite to have size selectivity or shape selectivity to certain molecules and thus zeolite is called as a molecular sieve.
Zeotype molecular sieves generated by replacing a portion or all of silicon (Si) and/or aluminum (Al) atoms of a zeolite molecule are also widely used in the industrial field. For example, zeotype molecular sieves in which anions are replaced with metal atoms serve as a catalyst for cracking petroleum. Besides, zeolites and zeotype molecular sieves have been reported to be useful as adsorbent, water-absorbing agent, gas-purifying agent, additives for detergent, ion exchanger, soil improving agent and carrier for sensor.
Zeolites and zeotype molecular sieves generally exist as fine powders. For practical application, it has been extensively studied that fine powders of zeolites or zeotype molecular sieves are attached to the surface of substrates such as glass, ceramic, polymer and metal.
As the simplest approach, it has been suggested that zeolite particles are attached to substrates via physical interaction by immersing substrates into the suspension containing zeolite crystals (L. C. Boudreau, J. A. Kuck, M. Tsapatsis, J. Membr. Sci., 152:41-59 (1999)). Since this attempt is to control the dispersion of zeolite particles by adjusting the rate of taking zeolites out of the suspension, zeolite particles are unlikely to form an even monolayer and likely to be detached from substrates due to their merely physical adsorption to substrates.
In addition, the method using compounds carrying at their both ends methyldimethoxysilyl groups (Me(MeO)2Si−) as spacers for zeolite-substrate linkages has been suggested (Z. Li, C. Lai, T. E. Mallouk, Inorg. Chem, 28:178-182 (1989)). According to this report, one methyldimethoxysilyl group of the spacer is initially attached to substrates and the resultant is then mixed with zeolite particles to induce covalent linkages between the other methyldimethoxysilyl group and zeolite particles. Even though this method shows higher attachment strength than that of the simplest immersion-involving method, the orientation of zeolite particles cannot be controlled and two methyldimethoxysilyl groups of the spacer are found to be attached to substrates, which interferes the formation of linkages between substrates and zeolite particles.
It has been reported that linkages between substrates and zeolites can be formed via multi-ionic bonds (L. C. Boudreau, J. A. Kuck, M. Tsapatsis, J. Membr. Sci., 152, 41-59 (1999)). Aminopropylgroups bound covalently on the surface of substrates are treated with hydrochloric acid to charge the surface with cations by ammonium ions and then treated with sodium polystyrene sulfate to convert charge of the surface to anions. Thin films of zeolites are prepared by repeating the two steps. However, such preparatory process requires at least six steps, and results in somewhat poor arrangement of zeolites and poor binding strength.
Moreover, it has been suggested that nuclei of zeolite particles are generated onto substrates and grown to directly synthesize zeolite films on the surface of substrates (J. C. Jansen, D. Kashchiev, A. Erdem-Senatalar, Stud, Surf. Catal., 85:215-250 (1994)). However, such attempt has limitations and shortcomings in the senses that it necessitates unchangeable substrate under conditions for zeolite synthesis and is unable to control the thickness of zeolite monolayer.
In recent, zeolites and zeotype molecular sieves has been researched as innovative materials following accomplishment of the synthesis of nano-scaled zeolites (G. A. Ozin, A. Kuperman, A. Stein, Angew. Chem. Int. Ed. Engl. Adv. Mater. 28:359 (1989)). Particularly, zeolites have been studied to be applied as a host for a three-dimensional memory material (G. A. Ozin, A. Stein, G. D. Stucky, J. P. Godber, J. Inclusion Phenom. 6:379 (1990)), a light energy storage device (M. Bodja, P. K. Dutta, Nature 362:43 (1993)); M. Sykora, J. R. Kincaid, Nature 387:162 (1997)); Y. Kim et al., J. Phys. Chem. 101:2491 (1997)), a nanoelectrode (D. R. Rolison, C. A. Bessel, Acc. Chem. Res. 33:737 (2000)), a quantum beam or point of semiconductor (N. Herron et al., J. Am. Chem. Soc. 111:530 (1989)), a molecular circuit (T. Bein, P. Enzel, Angew. Chem. Int. Ed. Engl. 12:1737 (1989)), a photosensitive device (G. Grubert, M. Stockenhuber, O. P. Tkachenko, M. Wark, Chem. Mater. 14:2458 (2002)), a luminant (G. Calzaferri et al., J. Mater. Chem. 12:1 (2002)), a nonlinear optical material (S. D. Cox, T. E. Gier, G. D. Stucky, J. Bierlein, J. Am. Chem. Soc. 110:2986 (1988)) or a laser luminant (U. Vietze et al., Phys. Rev. Lett. 81:4628 (1998)).
In order to find application of zeolites and zeotype molecular sieves as innovative material and to overcome shortcomings associated with conventional linking approaches described previously, the present inventors have already suggested assembly methods in which nano- or micro-scaled zeolite particles are organized into uniformly aligned, two- or three-dimensional compact structures (zeolite supercrystals) (A. Kulak, Y.-J. Lee, Y. S. Park, K. B. Yoon, Angew. Chem. Int. Ed. 39:950 (2000); S. Y. Choi, Y.-J. Lee, Y. S. Park, K. Ha, K. B. Yoon, J. Am. Chem. Soc. 122:5201 (2000); A. Kulak, Y. S. Park, Y.-J. Lee, Y. S. Chun, K. Ha, K. B. Yoon, J. Am. Chem. Soc. 122: 9308 (2000); G. S. Lee, Y.-J. Lee, K. Ha, K. B. Yoon, Tetrahedron 56:6965 (2000); K. Ha, Y.-J. Lee, H. J. Lee, K. B. Yoon, Adv. Mater. 12:1114 (2000); K. Ha, Y.-J. Lee, D.-Y. Jung, J. H. Lee, K. B. Yoon, Adv. Mater. 12: 1614 (2000); G. S. Lee, Y.-J. Lee, K. B. Yoon, J. Am. Chem. Soc. 123:9769 (2001); K. Ha, Y.-J. Lee, Y. S. Chun, Y. S. Park, G. S. Lee, K. B. Yoon, Adv. Mater. 13:594 (2001); G. S. Lee, Y.-J. Lee, K. Ha, K. B. Yoon, Adv. Mater. 13:1491 (2001); Y. S. Chun, K. Ha, Y.-J. Lee, J. S. Lee, H. S. Kim, Y. S. Park, K. B. Yoon, Chem. Comm. 17:1846 (2002); J. S. Park, G. S. Lee, Y.-J. Lee, Y. S. Park, K. B. Yoon, J. Am. Chem. Soc. 124:13366 (2002); J. S. Park, Y.-J. Lee, K. B. Yoon, J. Am. Chem. Soc. 126:1934 (2004); K. Ha, J. S. Park, K. S. Oh, Y. S. Zhou, Y. S. Chun, Y.-J. Lee, K. B. Yoon, Micropor. Mesopor. Mater. 72:91 (2004)). Furthermore, the present inventors have developed a complex comprising mono- or multi-layered zeolites linked to substrates and its preparation method (see Korean Pat. No. 335966 and PCT/KR00/01002).
The patent documents disclose processes for forming a multi-layered film of molecular sieves onto substrates in which: (1) a covalent-linked substrate-linker (intermediate 1) and a covalent-linked zeolite-linker (intermediate 2) are linked via functional groups at the ends of linkers; (2) substrates or zeolites are directly attached to one terminal of linkers covalently bound to substrates or zeolites via their other terminal, (3) a middle linker is incorporated between the intermediates 1 and 2 to adjust the length between substrates and zeolites, and (4) repeating steps described (1)-(3) to form multi-layered film of molecular sieves on substrates. Although such processes contribute to applicability of substrate-molecular size composites as innovative materials, the refluxing step for linking between substrates and linkers, zeolite crystals and linkers, linkers and linkers, or linkers and intervening linkers gives rise to lower energy efficiency, attachment rate, degree of lateral close packing (DCP) between zeolite crystals and strength of linkage between zeolites and substrates.
Throughout this application, various patents and publications are referenced, and citations are provided in parentheses. The disclosure of these patents and publications in their entities are hereby incorporated by references into this application in order to more fully describe this invention and the state of the art to which this invention pertains.